Automatic control system for rolling mills and adjustable dies



May 16, 1967 P. MASTERSON; JR 3,319,444 AUTOMATIC CONTROL SYSTEM FOR ROLLING MILLS AND ADJUSTABLE DIES 4 Sheets-Sheet 3 Filed Nov. 1-), 1964 m w m N O S i; Om-

.m 15; ON m INVENTORV James P Mosiersomdr. BY

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ORNEY May 16; 1967 J. P. MASTERSON, JR 3,319,444

CONTROL SYSTEM FOR ROLLING MILLS AND ADJUSTABLE DIES AUTOMATIC 4 Sheets-Sheet Filed Nov.

A mOP0 mPmDw L mwN ZOmIOZ m EN w.r 0 mOkaimgrsDi JOmFZOO mOPOE INVENTOR. James P Musierson, Jr. B

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United States Patent 3,319,444 AUTOMATIC CONTROL SYSTEM FOR ROLLING MILLS AND ADJUSTABLE DIES James P. Masterson, In, Wallingford, Conn., assignor to Allegheny Ludium Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania Filed Nov. 9, 1964, Ser. No. 409,766 13 Claims. (Cl. 72-8) This invention relates to the production of material by rolling through single or multiple stand rolling mills or by drawing through single or multiple dies of the kind having opposed die surfaces whose separation is adjustable. More particularly, the invention relates to an automatic system for controlling such mills or dies so as to produce a material of predetermined uniform gage thickness. v

As is known, many of the commonly-used commercial control systems for rolling mills are based on the premise that a mill screwdown or the like can be controlled accurately from a gage measurement taken several feet beyond the exit side of the mill. In such a system, the material, after reduction, progresses to the gage which may be several feet beyond the bite of the mill before any error present in the material thickness can be detected. This distance from the bite of the rolls to the gage is commonly referred to as transport distance. The time required for the material to reach the exit gage is denoted as transport time, while the time required to measure the strip gage is referred to as sensing time. Transport time and sensing time are major elements in developing error commands for the screwdown. Transport distances of five feet or more are common in rolling mills utilizing a single gage measurement taken beyond the exit side of the mill, meaning that such a system is not capable of detecting any deviation from the desired gage until five feet of material has passed from the bite of the mill rolls. The corrective signal is then transmitted to the mill screwdown; but the measuring gage does not detect the result of this action until five feet more of the material has passed through the mill. Thus, gage control systems of this type obtain error signals after the fact rather than before the fact. Such systems, while used extensively, cannot control the gage of the strip along its length within fine tolerances, particularly in the case of material entering the mill with fairly noticeable changes in gage.

In US. Patent Nos. 3,015,974, 3,054,311 and 3,121; 354, rolling mill control systems are disclosed in which, for a constant mill speed, the transport time is zero and the measuring time is essentially zero also. This means, in effect, that the system measures and controls the mill or other similar device directly at the bite of the mill. Such systems are based on the concept that the volume of material V coming out of the mill must be equal to the volume V entering the mill. Thus:

V1=V2 and L W G LgWzGg where L =length of material entering the mill; L length of material leaving the mill; G =gage of material entering the mill; G =gage of material leaving the mill; W =width of material entering the mill; and W =width of material leaving the mill.

It has been found that the ratio of the width of material W entering the mill with respect to the width of material W leaving the mill remains constant during a given pass. Accordingly, these factors may be eliminated ice As will be understood, the output gage of the strip or other workpiece is the factor to 'be controlled by the system. Therefore, predetermined desired output gage G is introduced into the system which alters the foregoing equation as follows:

At the same time, the use of desired output gage G rather than actual output gage G renders the system capable of control before the fact rather than after the fact. In other words, transport time and sensing time are eliminated; and the system need not wait until the material has progressed beyond the bite of the mill before recognizing or deciding on the necessary control operation.

It is necessary, in a gage control system based on the constant volume principle, to advance entry gage measurements through a shift register storage unit in synchronism with the movement of strip material into the mill. As the material to be gaged approaches the bite of the rolling mill rolls, the system generates a command signal which causes a comparison of desired input gage G with the actual measured value of input gage G to obtain an error signal in the manner described above. If an error signal is generated, it is transported to the mill screwdown which effects the desired correction; however there is an inherent screwdown reaction time or delay between the comparison of desired and actual input gages and actuation of the screwdown, Furthermore, this delay or screwdown reaction time is a constant for any particular corrective command signal regardless of mill speed.

In the systems shown in the aforementioned U.S. patents, a constant mill speed and negligible screw reaction time were assumed. This enabled the entry gage measurements to be advanced through the shift register storage unit by shift pulses which would vary in repetition rate as a linear function of strip speed, assuming that the speed was varied. At slower speeds than the assumed speed, the screwdown correction, if called for, would occur prior to the gaged material entering the roll bite. At speeds faster than the assumed speed, the correction would occur after the gaged material had entered the roll bite. To illustrate, let us assume that the screwdown reaction time is one-half second in a system such as that shown in the aforesaid patents. If the device measuring actual input gage G is five feet ahead of the roll bite of the mill, and if the mill speed is one foot per second, it will take five seconds for the material to travel from the gage measuring device to the roll bite. Under these circumstances, the electrical signal representative of desired input gage (T will have to be subtracted from that representative of actual input gage G after the strip has traveled four and one-half feet from the measuring device. This will allow for the required one-half second screwdown reaction time before the point on the strip 3 where the gage measurement was taken reached the roll bite.

If, now, the speed of the mill is doubled to two feet per second, it will take the strip material only two and onehalf seconds to advance from the gage measuring device to the bite of the rolls rather than five seconds as in the case given above. If the advancement of actual input gage measurements is a linear function of strip speed as in the aforesaid U.S. patents, they will again arrive at the subtraction circuitry after the strip has traveled four and one-half feet as in the previous cases, but this occurs only one-quarter second before the point on the strip at which gage measurements were taken reaches the roll bite. This, of course, is less than the fixed screwdown reaction time of one-half second, meaning that the point on the strip at which an entry gage measurement has been taken will have advanced six inches beyond the roll bite before the corrective action is taken.

While many rolling mills are operated at a constant speed, it is sometimes desirable or necessary to vary the speed of the strip passing through the mill, in which case the systems shown in U.S. Patents Nos. 3,015,974, 3,054,- 311 and 3,121,354 are not entirely satisfactory.

Accordingly, it is an object of this invention to provide a control system for rolling mills and adjustable dies based on the constant volume principle wherein the speed of the mill can be varied continually or intermittently without affecting the accuracy of the gage control achieved.

A more general object of the invention is to provide a rolling mill control system wherein material entry gage measurements are advanced through an entry gage or storage shift register unit as a non-linear function of strip speed, thereby compensating for the fixed screwdown reaction time mentioned above. In this respect, it will be appreciated that the invention has application in any rolling mill control system, whether based on the constant volume principle or otherwise, where entry gage measurements are advanced through a shift register assembly as the strip advances from a gage measuring point to the bite of the rolling mill rolls.

As will hereinafter be described, material entry gage measurements are advanced through successive stages of a shift register or the like by shift pulses derived from a counter. In one embodiment of the invention, the input to the counter comprises pulses derived from a pulse generated connected to a roll in contact with the moving strip. The repetition rate of these pulses, therefore, will vary as a linear function of strip speed. Likewise, if the counter is preset to a fixed number of input pulses for each output pulse, the output pulses will also vary as a linear function of strip speed, a condition which is undesirable with varying mill speeds for the reasons given above.

Therefore, in accordance with one embodiment of the invention, the preset of the counter is automatically varied inversely with respect to strip speed, thereby compensating for the fixed screwdown reaction time.

In another embodiment of the invention, the input to the counter comprises pulses derived from a variable frequency pulse generator. By varying the frequency of the output pulses from the pulse generator inversely with respect to incoming transport time, the repetition rate of the output pulses from the counter which shift the entry gage measurements through the shift register will also Vary inversely with transport time, again compensating for the fixed reaction time of the screwdown.

In still another embodiment of the invention, an output is derived from each successive stage of the shift register and connected to an associated contact on a stepping switch or the like having a rotary wiper brush adapted to switch out of the circuit successive shift register stages, starting from the last stage. Movement of the wiper brush, in turn, is controlled as a function of the speed of the mill, the higher the speed the more stages of the shift register which are switched out of the circuitry. In this manner, the time required for entry gage measure- 4 ments to advance through the shift register decreases as mill speed increases due to a decrease in shift register stages, thereby compensating for the fixed screwdown reaction time.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIGURES 1a and 1b form a composite overall schematic diagram of the gage control system of the invention;

FIG. 2 illustrates waveforms appearing at various points in the circuit of FIGS. 1a and 1b;

FIG. 3 comprises a series of waveforms illustrating the effect of varying strip speed on the operation of the invention;

FIG. 4 is a graph of strip speed versus inches of strip travel per shift pulse, showing the manner in which the present invention compensates for variations in strip speed;

FIG. 5 is a graph of strip speed versus frequency of the shift pulses in accordance with the present invention; and

FIG. 6 is a partial schematic circuit diagram illustrating another embodiment of the invention wherein the screwdown reaction time is compensated for by switching out of the circuitry successive shift register stages as mill speed increases.

Referring now to the drawings, and particularly to FIGS. 1a and 1b, a conventional rolling mill 10 is provided with pressure rolls 12 and 14 between which passes the material 16 being acted upon or processed in the mill. In the particular illustration given, the material 16 comprises a continuous strip which feeds off payoff reel 18 and is coiled onto take-up reel 20. However, the direction of movement of the strip material through the mill 10 may be reversed, whereupon the reel 20 will become the payoff reel and reel 18 will become thetake-up reel.

Positioned on either side of the mill 10 are a pair of gage heads 19 and 21, each of which supports a vertically movable roller 22 positioned above the strip as well as a fixed roller 24 below the strip. Connected to the vertically movable rollers 22 through likages 25 and 26 are servo systems 28 and 30, respectively. Only the servo system 28, enclosed by broken lines, is shown in detail herein, it being understood that the other servo system 30 is identical in structure and operation. As the strip 16 passes through the gage head 19, for example, the: gaging rollers 22 and 24 will be in rolling contact with. its opposite surfaces; and as the thickness or gage of thematerial varies, the upper gaging roller 22 will move up-- wardly or downwardly, depending upon whether the strip 16 increases or decreases in thickness. That is, when the thickness of the strip 16 increases, the gaging roller 22 and linkage 25 will move upwardly; whereas, when. the thickness of the sheet decreases, these members will move downwardly.

In order to sense the position of the gaging roller 22 and linkage 25, there is provided an electromechanical transducer, generally indicated at 32, adapted to produce an electrical output which varies in proportion to the movement of roller 22. The transducer includes a center or primary coil 34 which is connected to a source of alternating current 36. At either end of the primary or center coil 34 and coaxial therewith are a pair of secondary coils 38 and 40. A rod-shaped magnetically permeable core 42 is positioned axially inside the coil assembly and provides a path for the magnetic fiux linking the coils. Core 42 is connected to the linkage 25 whereby the coil will be moved upwardly or downwardly depending upon the direction of movement of the roller 22. In series with the primary winding 34 of transducer 32 is the primary winding 44 of a second electromechanical transducer 46 which is similar in construction to transducer 32 and includes a pair of secondary coils 48 and 50 as well as a movable, magnetically permeable core 52. In this case, however, the core 52 is connected through a mechanical linkage 54 to a lever 56 which is controlled by means of a cam 58. The earn 58, in turn, is connected through gear reducer 68 to a two-phase servomotor 62 having two phases or windings 64 and 66 included therein.

With reference to transducer 32, when the primary or center coil 34 is energized with alternating current from source 36, voltages are induced in the other two coils 38 and 40. These secondary coils are connected in series opposition, meaning that the two voltages in the secondary circuit are opposite in phase whereby the net output of the transformer is the diiference of the voltages. For one central position of the core, this output voltage will be zero. When the core 42 is moved from this central position, the voltage induced in the coil toward which the core is moved increases, while the voltage induced in the opposite coil decreases. This produces a difierential voltage output which with proper design varies linearly with a change in core position. The motion of the core in the opposite direction beyond the central position produces a similar linear voltage characteristic with the phase shifted 180. Opposition of transducer 46 is identical to that of transducer 32 and, thus, by proper positioning of the cores 42 and 52 in the respective transducers the cumulative or output voltage produced across their respective secondary windings can be made equal and opposite in phase. These secondary windings are connected in series dilferential across the primary winding 68 of an input transformer 7 0. Thus, when the output voltages produced across the secondary windings of the respective transducers are equal and opposite in phase, the voltage appearing across the primary winding 68 will be zero. If the cores 42 and 52 are initially positioned so that zero output voltage is produced across winding 68, and if core 42 is thereafter moved upwardly, the output voltages produced across the secondary windings of the transducers will no Longer balance, and 'a voltage will appear across winding 68. If the core 42 moves downwardly from a balanced condition, then a voltage will again appear across winding 68, but in this case it will be shifted in phase with respect to the voltage produced when it moved upwardly from the balanced condition. The voltages appearing across the secondary winding of transformer 70 are applied to an amplifier 72, the output of which is connected acros one of the windings 64 of the two-phase servomotor 62. The other winding 66 of servomotor 62 is connected as shown to a source of alternating current voltage 74 which is in phase with voltage source 36. In actual practice, the two voltage sources 36 and 74 will probably be the same, but are shown herein separately for purposes of explanation.

With the arrangement described, the servomotor 62 will rotate in one direction or the other, depending upon the phase of the signal applied through winding 64. This phase will, in turn, depend upon the relative positions of cores 42 and 52 in their respective transducers as was explained above.

The gear ratio of gear reducer .60 is on the order of two-hundred to one, meaning that servomotor 62 will have to make two-hundred revolutions before the cam 58 rotates through 360. The arrangement is such that if core 42 in transducer 32 moves upwardly, for example, motor 62 will rotate the cam 5-8 to lower core 52 in transducer 46 until the voltages at the secondaries of the transducers balance and the servomotor stops. That is, as the core of transducer 32 is moved upwardly =by roller 22 in response to an increase in the thickness of strip 16, the coupling is increased between its primary 34 and secondary winding 38, and the voltage applied to the amplifier 72 increases. With this increase in voltage, the servomotor -62 drives the core of transducer 46 downwardly until the output voltages at the respective secondary windings are equal and the voltage appearing across winding 68 of input transformer 70 is zero. At this point the motor stops, and what has actually been done is to convert an electrical signal proportional to the change in strip thickness into a proportional rotary motion of the servomotor 62. That is, any change in thickness of the strip 16 as it passes through the gage head will induce a proportional number of revolutions in the.

servomotor 62 until the two transducer outputs again balance. If the thickness of the strip 16 decreases and the core 42 moves downwardly, the phase of the signal applied to the servomotor 62 will be reversed, and the cam 58 will be rotated to lower the core 52 in transducer 46.

The servomotor 62 is also connected through a mechanical connection 76 to a binary digitizer, generally indicated at 78. The digitizer is essentially a rotary switching device for energizing particular relays which represent bits in a binary number. In the particular illustration given, the digitizer 78 will produce an electrical signal com-prising eleven binary output bits which appear on leads 80. For a full and complete description of the digitizer, reference may be had to US. Patent No. 3,056,208, assigned to the .assignee of the present application. Although the digitizer shown in that application produces a decimal rather than a binary output, the conversion from decimal to binary notation will be obvious to those skilled in the art. Thus, a binary numher A, for example, will be represented by (A A A A etc.) where A is the binary bit 2, A is the binary bit 2 A is the binary bit 2 A is the binary bit 2 and so on. Each of the binary bits is represented on leads 80 by an ON or OFF signal, representing a one or zero, respectively. in binary notation. Thus, if the output leads from the digitizer 78 representing the A and A bits are ON or one while all other leads are OFF or zero, it means that the output of the digitizer is 2+2 or 1+8 which is 9. Similarly, if only the A and A leads are ON or one while all other leads are OFF or zero, the signal represented is 2 4-2 or 2+4 which is 6. Also included in the servo system 28 is apparatus, not shown, for automatically zeroing the system when the two rollers 22 and 24 are in contact with each other. This apparatus form no part of the present invention, but is fully shown and described in the aforesaid US. Patent No. 3,056,208.

As shown in FIG. 1a, the servo system 30 is also connected through a mechanical linkage 82 to a second digitizer 84 having eleven output leads 86. The corresponding output leads from the digitizers 78 and 84 are each connected to a bit line, only one of said lines being shown in detail in FIG. 1b and identified as bit line 0. Thus, the A leads from .both digitizers 78 and 84 are connected to bit line 0, the A leads from each digitizer will be connected to bit line 1, the A leads from each digitizer will be connected to bit line 2, the A leads from each digitizer will be connected to bit line 3, and so on.

Included in the circuit is a mill drive direction selector 114 which, among other things, serves to control the mill drive, not shown, to selectively reverse the direction of strip movement through the mill. The mill drive direction selector also controls the digitizers 78 and 84 through leads 88 and 90, respectively. That is, when the strip is moving from left to right as shown in FIG. la, the selector 114 will serve to enable or switch on the digitizer 78 whereby binary bits will appear on leads 80. At the same time, the selector 114 applies a signal to lead 90 to disable or switch off the digitizer 84. When, however, the direction of strip movement is reversed (i.e., from right to left in FIG. la) digitizer '78 will be disabled while digitizer 84 is enabled to produce binary bits on output leads 86. Thus, only one set of binary bits from digitizer 78 or 84 will pass into the respective bit lines 8-10.

All of the bit lines 1-10 are identical in construction to bit line 0 shown in detail in FIG. 1b. With reference to this first bit line, it includes an electron valve 112 having its grid 90 connected to the A leads from each of the digitizers 78 and 84, it being understood that only one of these leads will be operative to pass ON signals at any time, depending upon the direction of strip movement through the mill. The cathode 121) of valve 112 is connected through lead 122 to one end of the secondary winding 124 of a transformer 126, the other end of the winding 124 being connected through a unidirectional current device 128 to ground. The primary winding 130 of transformer 126 is connected to a blocking oscillator 132 which receives a trigger-pulse from a gate circuit 134, the arrangement being such that the output of the blocking oscillator will be (a pulse each time a trigger pulse is received from gate circuit 134, however the output pulse of the blocking oscillator will be delayed with respect to the input trigger pulse from circuit 134. The delayed output pulse from the blocking oscillator is then coupled through transformer 126 to lead 122 to thereby apply a negative potential to the cathode 120 and enable the electron valve 112 to pass ON signals from digitizer 78 or 84 as the case may be. At all other times, however, the valve 112 is disabled. Lead 122 is also connected to the cathodes 120 in each of the remaining bit lines 1-1t1 where the action is the same as that described with respect to bit line 0.

The anode 136 of the tube 112 is connected to a source of anode voltage, designated B+, through the input winding 138 of a first circular magnetic core 140 in an entry gage memory unit or shift register assembly 141 which serves to store and advance successive actual entry gage measurements from valve 112 in synchronous correlation with the movement of strip 16. That is, each time the valve 112 is enabled by blocking oscillator 132, it feeds the instantaneous entry gage measurement in binary form from digitizer 78 or 84 to the storage unit which progressively advances these instantaneous measurements from one end of the unit to the other end, the time required to advance from one end to the other being equal to the time required for the strip 16 to travel from the rollers 22 and 24 to the bite of the mill 10.

Also included on the core 140 in the memory unit is a shift winding 142 and an output winding 144 which is connected through diode 146 and resistor 148 to the input winding 138 of a second circular magnetic core 150. As shown, a capacitor 152 is connected between the junction of diode 146 and resistor 148 and the other end of the output winding 144. Core 150 is identical to core 140 and includes an input winding 138, a shift winding 142 and an output winding 144. Core 150, in turn, is coupled to core 154 and this core, in turn, is connected to the next succeeding core in the chain. In the particular embodiment of the invention shown herein, it will be assumed that there are ten such cores connected in cascade, the last or tenth core being designated by the numeral 156.

Each of the cores 140, 150, 154, etc. is formed from permanent magnet material and may have flux remaining in either of two directions depending upon the last direction of the magnetizing current. In the illustration given, the input current in winding 138 can cause flux to flow in core 140, for example, in a clockwise direction while the shift current in winding 142 can cause flux in the counterclockwise direction. Current will flow in the output diode 146 only when the flux changes from clockwise to counterclockwise direction. Thus, a one or ON bit can be stored in the first core 140 by passing current through the input winding 138. The one or ON bit can then be transferred to the second core by passing current through the shift winding 142. As shown, all of the shift windings 142 are connected in series to lead 158 which, in turn, is connected to the output of gage circuit 134. Consequently, all of the cores in the chain are shifted simultaneously. When a shift pulse is applied to the shift windings 142, a one or ON bit in the first core 140, for example, will be transferred to the second core 150. As the flux changes, the diode 146 conducts and stores a charge in the capacitor 152. Before the capacitor 152 can discharge, however, the core will have already received a shift pulse to transfer its information onto core 154. Thus, when the capacitor 152 does discharge, the information which was stored on the first core is transferred to the second core 150 by action of the capacitor 152 discharging through the input winding 138 of this core. Information can flow only one way due to the diode and due to the ratio of turns between the input and output windings. Thus, the capacitors 152 act as a temporary storage medium while the cores are reset to zero. If there is no input current before the next shift current pulse, the first core will be in the zero state with counterclockwise flux. Hence, the shift current cannot change the flux, no current will charge the capacitor, and the following core will remain reset, thus shifting the zero or OFF binary bit from the first core to the second core.

With the arrangement described, each bit will be transferred from one core to the other until the final core 156 is reached. The output winding 144 of this core is then connected through lead 160 to a binary subtractor 162 which also receives the outputs from the other bit lines 1-10. As the input gage of the strip material varies, this variation will be detected by the servo system 28 so that the output of digitizer '78, for example, will be constantly changing, assuming that the input gage is also changing. However, by virtue of the fact that the electron valve 112 conducts only at periodic intervals, samples of the input gage will be passed through bit lines 0410 at periodic intervals also. As will hereinafter be explained, a sample of the input gage is passed to the cores 141), 1541, 154, etc. each time the strip 16 moves through 5.4 inches of travel. Since there are ten such cores connected in cascade, the strip will have to travel fifty-four inches before the output information arrives at the binary subtractor 162.

Reverting again to the rolling mill 10, input strip length (L is sensed by equipment similar to that described in US. Patent No. 2,982,158, namely a pulse generator 164 and a demodulator unit 166. Similarly, output strip length (L is sensed by a pulse generator 168 and demodulator unit 170. As shown, the outputs of the demodulators 166 and 170 are connected through switch means 172 to leads 174 and 176. The switch means 172 is controlled by the mill drive direction selector 114, the arrangement being such that when the strip 16 is travelling from left to right, the output of pulse generator 164 which represents input strip length (L is connected to lead 174, and the output of pulse generator 168 which represents output strip length (L is connected to lead 176. When, however, the direction of strip travel through the mill is reversed, the switch 172 will reverse the connections between the demodulators 166 and 170 and the leads 174 and 176. That is, when the strip is travelling from right to left, the output of pulse generator 168 will then represent input strip length (L so that the demodulator 170 will then be connected to lead 174 rather than lead 176. Similarly, under the conditions described, the output of pulse generator 164 will represent the output strip length (L so that the demodulator 166 will now be connected to lead 176 rather than lead 174.

For purposes of explanation, it will be assumed that the strip is travelling from left to right so that the output of pulse generator 164 is connected to lead 174 while the output of pulse generator 168 is connected to lead 176. Connected to the lead 174 is another lead. 178 which applies the pulses or oscillations representing the input strip length (L to a first L counter 188 which may, for example, be of the conventional flip-flop type comprising a plurality of multivibrators connected in cascade. In accordance with the present invention, the counter 180 is variably preset by means of an automatic presetting network 250, hereinafter described in detail. For purposes of explanation, however, it will be assumed in the following discussion that the counter 180 is permanently preset whereby it will trigger multivibrator 182 to produce an output pulse whenever the counter 180 reaches the count to which it was preset. In the illustration given, the counter 180 will be preset to trigger multivibrator 182 through switch 252 each time the input strip moves through 5.4 inches. Thus, assuming that the gate 134 is not disabled by a synchronizer 184, hereinafter described, a pulse from circuit 182 will pass through the gate 134 to the reset windings 142 on cores 140, 150, etc. and also to the blocking oscillator 132. The output pulse from the blocking oscillator 132, however, will be delayed with respect to that on lead 158 directly from gate 134, the arrangement being such that each of the cores 140, 150, etc. will shift the information stored therein before new information is fed into the system from valve 112.

The pulses or oscillations on leads 174 and 176 are also passed to gate circuits 190 and 192, respectively. The output of gate circuit 190 is then passed to a second L counter 194, the count of which is preset by means of a G preset circuit 196. The L counter 194, like counter 180, may comprise any of the wellknown types having a series of cascade-connected multivibrators. As is Well known to those skilled in the art, a counter of this type may be preset by a series of switch closures to count any desired number of oscillations before producing an output pulse. The circuit 196, therefore, comprises a plurality of switches which may be closed to preset the counter 194 to count the desired number of oscillations.

When the desired number of oscillations or pulses are counted by counter 194, it will produce an output to trigger the synchronizer 184 through multivibrator 198. At this point, the synchronizer will then disable the gate 134 through lead 200 while enabling the parallel binary subtractor circuit 162 through lead 292 to perform a binary subtraction. At the same time, the synchronizer 184 will block gates 190 and 192 through lead 204.

Reverting, now, to gate 192, its output is passed through lead 206 to an L counter 208 which will produce a binary output on tens leads 211) which is proportional to the number of oscillations or pulses counted by the L counter. The L counter is of the well-known type comprising a plurality of cascaded flip-flop circuits and is reset to begin counting from zero by a signal from synchronizer 184 through lead 212. At the same time the L counter 208 is reset, the L counter 194 is also reset by synchronizer 184 through lead 207, substantially as shown.

It will be remembered that an error signal proportional to the deviation in gage from a desired output gage is derived from the equation:

in order to obtain the correct error signal.

The factor is calculated as follows: It will be remembered that the second L counter 194 may be preset to count any number of pulses or oscillations by an appropriate number of switch closures in circuit 196. By setting the switch 10 closures so that the desired output gage G is equal in magnitude to L the error equation becomes:

Error: G L

In other words, the L counter 194 is set to trigger multivibrator 198 whenever L is equal to 6 When this occurs, the synchronizer 184 is actuated by the signal from multivibrator 198 to disable the gates 190 and 192 through lead 204 whereby both the L counter 194 and the L counter 208 stop counting. The output of the L counter at this instant then represents the factor or the desired calculated input gage E At the same time, the synchronizer enables the subtractor 162 to perform a parallel binary subtraction of the calculated desired input gage (G from the actual input gage at the bite of the mill (G to produce a binary output error signal schematically illustrated by the lead 214.

While the subtraction process is being performed, the synchronizer 184 blocks gate 134 so that no further information can pass through bit lines 0-10 during the subtraction process. After the subtraction process is then completed, the synchronizer will reset the L and L counters 194 and 208 through leads 207 and 212 and will enable the gates 190 and 192 to pass L and L pulses or oscillations to the counters to begin a new cycle. In this way, samples of the error signal (G G are obtained at spaced points along the strip 16, and the number of samples taken is dependent upon the preset value of G in switch closure circuit 196'. That is, circuit 196 determines the number of oscillations (i.e., the length of the strip) required to produce the signal to trigger the synchronizer 184; and this, in turn, depends upon the desired value of G Operation of the system may possibly best be understood by reference to FIG. 2 where waveform A represents the oscillations (L on lead 174. These oscillations, when fed to the first L counter 1 will cause the multivibrator 182 to produce an output pulse to gate 134 after every 5.4 inches of strip travel, assuming that the gaging rollers 22, 24 are five feet from the bite of rolls 12 and 14 and the strip speed is sixty feet per minute. The necessity for this relationship of the pulses with respect to strip travel will hereinafter be explained. The pulses in waveform B, then, are those which are passed through windings 142 in the cores 140, 150, etc. to shift the cores and advance the information through the memory unit each time the strip travels 5.4 inches. The output of the blocking oscillator 132, on the other hand, is represented by waveform C in FIG. 2 where the pulses have the same frequency as those in waveform B but are delayed with respect to the pulses in waveform B. Thus, as was mentioned above, the cores are first shifted to advance information to the memory unit, followed by the introduction of new information into the unit from valve 112.

During the time that waveforms B and C are being generated, the waveform A is fed also to the second L counter 194 which is preset by circuit 196. After the L counter 194 has counted a predetermined number of pulses or oscillations in waveform A determined by the setting of circuit 196, it will trigger multivibrator 198 to produce an output pulse 209 in waveform D of FIG. 2.

The pulse 299 in waveform D then actuates the synchro- T Waveform G from the synchronizer 184 is fed through leads 200 and 204 to gates 134, 196 and 192. This waveform includes a pulse 215 which starts at time T and persists for a short time after T thereby disabling the gates 134, 190 and 192 and preventing the feed-in of information to the cores 140, 150, 154, etc. as well as the counters 194 and 208 during the period of subtraction.

The output of the binary subtractor 162 on lead 214 is a binary signal having a magnitude proportional to the difference between the actual measured input gage (G and the calculated desired input gage (6 This signal is passed through a dead zone and alam set circuit 216 and a time control circuit 218 to the mill screwdown control 220. Circuit 218 controls the period during which the screwdown is operative. If the output of the subtractor 162 indicates that the gage is above G a signal will be fed on lead 222 to the mill screw control 224 to lower the upper roll 12. Similarly, if the output of the subtractor 162 indicates that the gage is below 6 a signal will be fed on lead 226 to the screw control 224 to raise the roll 12. Also connected to the mill screwdown control circuit 220 are two alarms 228 and 236. Alarm 228 will be actuated to signal the operator that the error signal is above a predetermined magnitude while alarm 230 will signal the operator that the error signal is below a predetermined magnitude. Included in the system is switching means, not shown, enabling the operator to place the screw control 224 on either manual or automatic operation wherein the output of the subtractor 162 controls. This enables the operator to control the mill by manual means until the alarm ceases, indicating that the correct G information has arrived at the outputs of bit lines -10.

As was mentioned above, the gaging rollers 22 and 24 are spaced five feet ahead of the bite of the rolls 12 and 14; however the counter 180 is preset to produce an output pulse to gate 134 after every 5.4 inches of strip travel. Since there are ten stages or cores in the shift register assembly 141, and since the gaging rollers 22 and 24 are spaced five feet (i.e., sixty inches) ahead of the bite of the rolls, it might be assumed that a pulse should be produced by counter 180 each time the strip travels six inches rather than 5.4 inches. This assumption would hold true except for the fact that there is a fixed reaction time of the screwdown 220, 22.4, which in the present case, is assumed to be one-half second. In other words, it will take the screwdown mechanism one-half second to effect the desired correction after a subtraction has been performed in circuit 162 and the error signal arrives at circuit 220.

The effect of the screwdown reaction time for different strip speeds can best be understood by reference to FIG. 3 where waveform A comprises the output of counter 180 in the case where it is preset to produce an output pulse each time the strip has traveled six inches. In this case, each pulse will arrive at the output end of the shift register 141 when the corresponding increment on which a gage measurement is taken is at the bite of the mills. Since, however, there is an inherent screwdown reaction time of one-half second, and assuming a speed of sixty feet per minute, six inches of strip travel will have elapsed between the time that the correct increment is at the bite of the mills and the time that the corrective action has been taken. Consequently, when the corrective action of the screwdown occurs, it will be taken on an increment of strip which trails the correct increment by six inches.

Accordingly, in order to compensate for this effect, the counter 180 is preset to produce an output pulse for every 5.4 inches of strip travel, meaning that gage measurements will reach the end of the shift register assembly 141 when their corresponding strip increments on which the measurements were taken are six inches ahead of the bite of the rolls. This is shown by waveform A in FIG. 3. Since, however, the reaction time of the screwdown is one-half second, and since the strip will travel six inches in one-half second, it will be appreciated that the screwdown reaction time is compensated for and that the correct increment along the length of the strip will arrive at the bite of the rolls when the corresponding corrective action is taken.

Let us assume now, that the speed of the strip is increased to feet per minute; and that a pulse is produced at the output of counter during every six inches of strip travel as in the case assumed for waveform A. In this case, however, five feet of strip will travel between the gaging rollers 22, 24 and the bite of the rolls in two and onehalf seconds rather than five seconds, each second representing two feet of strip travel. In waveform B, it can be seen that under these circumstances the screwdown delay time of one-half second will represent strip travel of one foot. Under these circumstances, counter 180 must produce an output pulse for each 4.8 inches of strip travel as shown by waveform B in order to compensate for the one-half second screwdown delay time representing one foot or twelve inches of strip travel.

Again, if the speed of the strip is increased to onehundred eighty feet per minute and the counter 180 produces an output pulse during every six inches of strip travel, the screwdown delay time of 0.5 second will represent 1.5 feet of strip travel. Under these circumstances, the counter 1841 must produce an output pulse during every 4.2 inches of strip travel in order to compensate for the one-half second screwdown reaction time representing strip travel of 1.5 feet.

With reference to FIG. 4, it will be seen that inches of strip travel per pulse at the output of counter 180 will vary linearly with strip speed in order to compensate for the fixed screwdown reaction time. The frequency or repetition rate of the pulses at the output of counter 180, however, will vary non-linearly with strip speed as shown by the graph of FIG. 5. This means, in effect, that either the preset of counter 180 must be varied linearly with strip speed, or the frequency of the input pulses to the counter varied as a non-linear function of strip speed in accordance with the graph of FIG. 5.

Apparatus for automatically varying the preset of counter 180 is shown in FIG. 1b and comprises a digital-toanalog converter 254 adapted to produce a steady-state signal on lead 256 which varies as a function of the frequency of the pulses produced by pulse generator 164 or 168, as the case may be. This steady-state signal on lead 256 varies linearly with strip speed and is applied to the automatic presetting network 250 to thereby vary the preset of the L counter 180. The automatic presetting network 250 may, for example, comprise a switching network, controlled by the signal on lead 256, for presetting the counter 180 for the desired number of input pulses per output pulse, depending upon the speed of the strip material.

As an alternative to the automatic presetting network 250, the switch 252 may be reversed from the position shown in FIG. 1b whereby a second L counter 180' is connected to the input of multivibrator 182. The input to the L counter 180 is from a variable frequency oscillator 258 (FIG. 1a) and lead 260. The output frequency of oscillator 258 is controlled by means of a tapered rheostat 262 the wiper arm of which is positioned through mechanical linkage 263 as a function of the main mill speed selector control rheostat 298 connected to motor control circuit 264. As the speed of the rolling mill is increased and the wiper arms on rheostats 262 and 298 advanced, the output frequency of the variable frequency oscillator 258 will also vary, but non-linearly in accordance with the curve shown in FIG. 5. As will be understood, the non-linearity is produced by virtue of the taper on rheostat 262. Consequently, the output pulses from L counter 180' will also vary non-linearly in accordance 13 with the graph of FIG. to effect the desired correction and thereby compensate for the fixed screwdown reaction time.

With reference now to FIG. 6 still another embodiment of the invention is shown in which the major portion of the elements corresponding to those shown in FIGS. 1a and 1b are identified by like reference numerals. In this case, however, the entry gage memory units 141-0 and 141-1 for both the 0 and 1 bit lines are shown. Furthermore, the ten cores in memory unit 141-0 are identified as C1-0 through C-0 and those in memory unit 141-1 are identified as C1-1 through C16-1. Of course, in an actual installation there are eleven such memory units, only two of such units being shown herein for purposes of explanation.

In this embodiment, the preset of the L counter 180 is fixed, meaning that the shift pulses on lead 158 applied to the cores in the memory units 141-0 and 141-1 vary in direct proportion to strip speed. Furthermore, the variable frequency pulse generator 258 is not employed, nor is the L counter 180'. Consequently, the shift pulses will appear as those in waveforms A, B and C in FIG. 3.

In order to compensate for the fixed screwdown reaction time, one or more of the cores in each memory unit 141-0 and 141-1 are switched out of the circuitry in sequence as the speed of the mill is increased, thereby compensating for the fixed screwdown reaction time. In this respect, it will be noted that the output of core C10-0 is connected through lead 270 to a first contact K10 on a bank B of a rotary stepper switch assembly 272. Similarly, the output of core C9-0 is connected through lead 274 to contact K9 on bank E the output of core C8-0 is connected through lead 276 to contact K8 on bank B and the output of core C7-0 is connected through lead 278 to contact K7 on bank B In a similar manner, the outputs of cores C10-1, C9-1, C8-1 and 07-1 are connected to contacts K10, K9, K8 and K7, respectively, on bank B of assembly 272 through leads 280, 282, 284 and 286. The movable wiper brushes 288 and 290 for banks B and B respectively, are connected through a mechanical linkage 292 to a rotary stepping switch actuator 294 which will advance the Wiper brushes 288 and 290 from one contact point to the next successive contact point along the direction of arrows 296 each time an actuating signal is applied to the actuator 294. As will be understood, the rotary stepping switch 272 will have eleven banks of contacts thereon in an actual installation, only two of such banks being shown for the two memory units 141-0 and 1411.

The actuator 294 'is controlled to either cause the wiper brushes 288 and 290 to advance or reverse by means of four limit switches L-10, L-9, L-8 and L-7 on the main speed rheostat 298 which, through motor control circuit 264, controls the speed of the drive motor 266 and rolls 12 and 14. With the wiper brush 300 on rheostat 298 in the position shown, the mill will be running at minimum speed and limit switch L-10 will be tripped to cause actuator 294 to position wiper brushes 288 and 290 on contacts K10 of banks B and B respectively. As the speed of the mill is increased by rotating the wiper brush 300 on rheostat 298 in a counterclockwise direction, limit switch L-9 will be tripped to cause actuator 294 to advance wiper brushes 288 and 290 to contacts K9.

The wiper brushes 288 and 290 are connected to the subtractor 162 as shown, which subtractor corresponds to that shown in FIG. 1b. Consequently, when the Wiper brushes 288 and 290 are advanced to contacts K9, the cores C10-0 and C10-1 are switched out of the circuitry, meaning that the time required for the gage information to pass through the memory units 141-0 and 141-1 will be reduced. Similarly, if the speed of the mill is further increased to the point where limit switch L-8 is tripped, the actuator 294 will move the wiper brushes 288 and 290 to contacts K8, whereupon both cores C9-0 and C10-0 will be switched out of the circuitry as will cores 09-1 14 and C10-1. The result, of course, is that the time re quired for the gage information to pass through the memory units 141-0 and 141-1 is now further reduced.

In the present case, provision is made for switching out of the circuitry only the last four cores of each memory unit; however this number may be increased to suit requirements. As the speed of the mill is decreased by rotating the wiper brush300 on rheostat 298 in a clockwise direction, the wiper brushes 288 and 290 follow to successively switch additional cores into the circuitry, thereby increasing the time required for gage information to pass through the memory units. The result is that the time required for gage information to arrive at subtractor 162 varies non-linearly with strip speed to thereby compensate for the fixed screwdown reaction time.

Although the invention has shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which travelling strip material passes, time delay means for delaying electrical signals representing entry gage measurements taken at a point ahead of the bite of the mill as the strip moves from the point of measurement to the bite of the rolls, circuit apparatus connected to the output of said time delay means for controlling said screwdown mechanism, and means for varying the delay time of said time delay means as a nonlinear function of the speed of said strip to insure that for any strip speed the entry gage measurements will reach the output end of the time delay means before the corresponding increments of the strip on which the gage measurements were taken reach the bite of the rolls.

2. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which travelling strip material passes, a shift register assembly having a plurality of stages through which entry gage measurements taken at a point ahead of the bite of the rolls are advanced as the strip moves from the point of measurement to the bite of the rolls, means connected to the output of said shift register assembly for controlling said screwdown mechanism, and means including a counter for producing shift pulses for said shift register assembly which vary in frequency as a non-linear function of the speed of said strip to insure that for any strip speed the entry gage measurements will reach the output end of the shift register assembly before the corresponding increments of the strip on which the gage measurements were taken reach the bite of the rolls.

3. The rolling mill control system of claim 2 and including apparatus, responsive to the speed of said strip, for varying the preset of said counter.

4. The rolling mill control system of claim 2 wherein the means for producing shift pulses includes a source of oscillatory voltage which varies in frequency as a function of the speed of the strip and which is connected to the input of said counter.

5. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which travelling strip material passes, a shift register assembly having a plurality of stages through which entry gage measurements taken at a point ahead of the bite of said rolls are advanced as the strip moves from the point of measurement to the bite of the rolls, and means including a counter for producing shift pulses for said shift register assembly which vary in frequency as a non-linear function of the speed of said strip to insure that for any strip speed the entry gage easurements will reach the output end of the shift register assembly before the corresponding increments of the strip on which the gage measurements were taken reach the bite of the rolls, the time between arrival of an entry gage measurement at the output end of said shift register and arrival at the bite of the rolls of the corresponding increment of strip at which the gage measurement was taken 'being substantially equal to the reaction time of said screwdown mechanism.

6. In a rolling mill control system of the type in which material entry gage measurements taken at a point ahead of the bite of the mill rolls are advanced through successive stages of a shift register assembly as the strip moves from the point of measurement to the bite of the rolls; the combination of means including a counter for producing shift pulses for said shift register assembly which vary in frequency as a non-linear function of the speed of said strip to thereby compensate for a fixed reaction time of the screwdown of said mill and insure that the entry gage measurements reach the end of the shift register assembly before the corresponding increments of the strip reach the bite of the rolling mill rolls by an amount substantially equal to the reaction time of said screwdown.

7. In a rolling mill control system of the type in which the spacing between opposed rolls is varied by a screwdown mechanism and wherein entry gage measurements of strip material passing between the rolls are taken at a point ahead of the bite of the rolls and advanced through successive stages of a shift register assembly as the strip moves from the point of measurement to the bite of the rolls; the combination of means including a counter for producing shift pulses, means for producing an oscillatory signal which varies in frequency as a function of the speed of said strip material, a demodulator electrically connected to said last-named means for producing a steadystate signal which varies in magnitude as a function of the frequency of said oscillations and hence the speed of said strip material, and an automatic presetting network operatively connected to said demodulator for automatically establishing the preset of said counter such that the frequency of the shift pulses produced by the counter will vary as a non-linear function of strip speed to thereby compensate for the fixed screwdown reaction time of said screwdown mechanism.

8. In a rolling mill control system of the type in which the spacing between opposed rolls is varied by a screwdown mechanism and wherein entry gage measurements of strip material passing between the rolls are taken at a point ahead of the bite of the rolls and advanced through successive stages of a shift register assembly as the strip moves from the point of measurement to the bite of the rolls; the combination of tachometer means operatively associated with said strip material for producing oscillations which vary in frequency as a function of the speed of the strip material, a counter responsive to said oscillations for producing shift pulses for said shift register assembly, a demodulator operatively connected to said tachometer means for producing a steady-state signal which varies in magnitude as a function of the frequency of said oscillations, and an automatic presetting network for said counter responsive to said steady-state signal for automatically varying the preset of the counter whereby the frequency of said shift pulses will vary as a non-linear function of the speed of the strip material to thereby compensate for the fixed reaction time of said screwdown mechanism.

9. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which travelling strip material passes, a shift register assembly having a plurality of seriallyconnected stages through which entry gage measurements taken at a point ahead of the bite of the rolls are advanced as the strip material moves from the point of measurement to the bite of the rolls, means responsive to entry gage measurements advanced through the shift 16 register assembly for controlling said screwdown mechanism, and switch means for connecting a successively fewer number of the stages in the shift register assembly to said controlling means as the speed of the strip material passing through the rolls increases.

10. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which travelling strip material passes, a shift register assembly having a plurality of serially-connected stages through which entry gage measurements taken at a point ahead of the bite of the rolls are advanced as the strip material moves from the point of measurement to the bite of the rolls, means responsive to entry gage measurements advanced through the shift register assembly for controlling said screwdown mechanism, means for producing shift pulses for said shift register assembly which vary in frequency as a linear function of the speed of said strip and switch means for connecting a successively fewer number of the stages in the shift register assembly to said controlling means as the speed of the strip material passing through the rolls increases, whereby the amount of travel of the strip during the advancement of gage measurements through the shift register assembly decreases as the speed of the strip increases.

11. In a rolling mill control system, a screwdown mechanism for varying the spacing between opposed rolling mill rolls between which traveling strip material passes, a shift register assembly having a plurality of seriallyconnected stages through which entry gage measurements taken at a point ahead of the bite of the rolls are advanced as the strip material moves from the point of measurement to the bite of the rolls, means responsive to entry gage measurements advanced through the shift register assembly for controlling said screwdown mechanism, means for producing shift pulses for said shift register assembly which vary in frequency as a linear function of the speed of said strip material, stepping switch means having a plurality of contacts thereon adapted to be successively engaged by a wiper brush device, means connecting said wiper brush to said controlling means, electrical conductors connecting the outputs of at least some to the successive serially-connected stages of the shift register assembly to successive contacts on said stepping switch means, and means for advancing said wiper brush device as the speed of said strip material increases to thereby disconnect from the controlling means successive stages of the shift register assembly as the speed of said strip material increases.

12. In a rolling mill control system of the type in which the spacing between opposed rolls is varied by a screwdown mechanism and wherein entry gage measurements of strip material passing between the rolls are taken at a point ahead of the bite of the rolls and advanced through successive stages of a shift register assembly as the strip moves from the point of measurement to the bite of the rolls; the combination of means including a counter for producing shift pulses for said shift register assembly, a variable frequency oscillator connected to the input of said counter whereby the oscillations produced by said oscillator will be counted by the counter, and means for varying the output frequency of said oscillator as a nonlinear function of the speed of said strip material whereby the frequency of the shift pulses will compensate for the fixed reaction time of said screwdown mechanism.

13. The combination of claim 12 wherein the output frequency of said variable frequency oscillator and the speed of said strip material are controlled from a common potentiometer.

No references cited.

WILLIAM W. DYER, IR., Primary Examiner.

G. A. DOST, Assistant Examiner. 

1. IN A ROLLING MILL CONTROL SYSTEM, A SCREWDOWN MECHANISM FOR VARYING THE SPACING BETWEEN OPPOSED ROLLING MILL ROLLS BETWEEN WHICH TRAVELLING STRIP MATERIAL PASSES, TIME DELAY MEANS FOR DELAYING ELECTRICAL SIGNALS REPRESENTING ENTRY GAGE MEASUREMENTS TAKEN AT A POINT AHEAD OF THE BITE OF THE MILL AS THE STRIP MOVES FROM THE POINT OF MEASUREMENT TO THE BITE OF THE ROLLS, CIRCUIT APPARATUS CONNECTED TO THE OUTPUT OF SAID TIME DELAY MEANS FOR CONTROLLING SAID SCREWDOWN MECHANISM, AND MEANS FOR VARYING THE DELAY TIME OF SAID TIME DELAY MEANS AS A NONLINEAR FUNCTION OF THE SPEED OF SAID STRIP TO INSURE THAT FOR ANY STRIP SPEED THE ENTRY GAGE MEASUREMENTS WILL REACH THE OUTPUT END OF THE TIME DELAY MEANS BEFORE THE CORRESPONDING INCREMENTS OF THE STRIP ON WHICH THE GAGE MEASUREMENTS WERE TAKEN REACH THE BITE OF THE ROLLS. 